What is “Junk” DNA?
Junk DNA, a term first used in the 1960’s, was used to describe the non-coding sequences of DNA. According to News Medical, in a Nature review, Leslie Orgel and Francis Crick stated that junk DNA “had little specificity and conveys little or no selective advantage to the organism”. Scientists were unable assign any sort of function to these sequences, therefore, they thought this noncoding strand had no function.
According to PSRAST, if these sequences thought to be “Junk” DNA were in fact junk, the nucleotides in the DNA should be completely random, however, it has been found that the sequence of these are not random at all. Because of this, scientists now believe this “Junk” DNA must contain some kind of coded information.
What Does It Do?
Scientists now believe that this “Junk” DNA has various regulatory rules. This non-coding DNA influences the coding DNA in an important way. One reason scientists believe this DNA has regulatory functions is because the sequences of the “Junk” DNA are inherited and some repetitive patterns are associated with increased risk for cancer. This DNA can mutate rapidly in response to the cancer, so it has been speculated that it may contribute to the regulation of cellular processes (PSRAST).
According to PSRAST, there was a study done by Harvard Medical School on the “Junk” DNA. The study found that a “Junk” DNA strand regulated the activity of nearby genes. Most genes make proteins, but these genes work by being switched on. When the genes are switched on, it blocks the activity of an adjacent gene. A statement from the study was that “the researchers have evidence that the new gene, SRG1, works by physically blocking transcription of the adjacent gene, SER3.” Another study, called the ENCODE project, was conducted and the result was “three quarters of the non-coding DNA in the human genome did undergo transcription and that almost 50% of the genome was available to the proteins involved in genetic regulation such as transcription” (News Medical).
Many scientists believe that this “Junk” DNA helps regulate the cell and contributes to many human characteristics. When a gene is switched on, it can have a big impact on the size and shape of an organism. According to NPR, “there are many genes that have changed remarkably little between a mouse and a human, for example, and yet they behave differently within the cell, and that’s largely due to the way they are regulated differently.”
In another study from NPR, scientists were trying to find a gene sequence that involved brain development. When scientists believed they found such sequence they took the chimp sequence and the human sequence and injected it into mouse embryos. The study showed that the human DNA turned on gene activity in the neural stem cells. The mouse cells injected with the human sequence were approximately 12% bigger, before birth, according to a report in the journal Current Biology. What makes this study important was that this sequence that involves brain development was found on what was previously thought of as “Junk” DNA. This is just another study to support researchers idea’s that the “Junk” DNA has regulatory functions.
The “Junk” DNA may also play an important part in the creation of human limbs. A study was conducted at Yale where researchers looked for DNA sequences that were different in humans and other animals. According to NPR, scientists took this human DNA sequence that was different from other animals and injected it into a mouse egg. After injection, he wanted to see what cells became active as the embryo developed and he found that this sequence of “Junk” DNA looked like a regulatory gene because it seemed to switch genes on and off.
So, Is It Really Junk?
Many of these scientists agree that many of the differences between humans and other primates come from these “Junk” DNA sequences. Previously, these sequences were thought of as “Junk” because researchers could not find any function that these genes do. Now, with more technology and scientific advancements, scientists are now getting evidence that these sequences do, in fact, have some function, cell regulatory functions.